. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. EPIDERMAL STRUCTURES. 99 with the hair follicles, while a system of smooth muscle fibres (especially strong in porcupines) serves to erect the hairs. Closely related to hair are the nails, claws, and hoofs of mammals, and the horn of sheep, goats, and cattle; in fact, these structures may be regarded as com- posed of agglutinated hairs. Somewhat different in character are the scales which cover the body in the pangolins (manids), and are found on the tail of the rodent Anomalurus, although these are both of epidermal origin.
. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. EPIDERMAL STRUCTURES. 99 with the hair follicles, while a system of smooth muscle fibres (especially strong in porcupines) serves to erect the hairs. Closely related to hair are the nails, claws, and hoofs of mammals, and the horn of sheep, goats, and cattle; in fact, these structures may be regarded as com- posed of agglutinated hairs. Somewhat different in character are the scales which cover the body in the pangolins (manids), and are found on the tail of the rodent Anomalurus, although these are both of epidermal origin. True dermal bones in the skin occur only in the armadillos among recent forms, where they form an armor upon the dorsal sur- face of the body. In the fossil glypto- dons the body was enclosed in a similar bony case, while some extinct cetacea possessed dermal Fig. io8. Hair tracts on early cat embryos, after Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Kingsley, J. S. (John Sterling), 1854-1929. New York, H. Holt and Company
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